Closed loop stepping motor servo mechanism

ABSTRACT

A servo - mechanism utilizing a pulse motor comprises a comparator amplifier for producing an output corresponding to the difference between an input signal voltage and a feedback voltage, a signal conversion circuit for converting the output from the comparator amplifier into two bit level signals, and a pulse motor driving circuit for controlling the direction of the pulse motor in accordance with one of the two bit level signals and for controlling the start and stop of the pulse motor in accordance with the other of the two bit level signals.

United States Patent [1 1 Ohta [ CLOSED LOOP STEPPING MOTORSERVO-MECHANISM [75] Inventor: Susumu Ohta,Toky0,Japan [73] Assignee:Yokogawa Electric Works, Ltd.,

Tokyo, Japan Filed: Apr. 28, 1971 Appl. No.: 138,189

[30] Foreign Application Priority Data Apr. 30, 1970 Japan 45/37330 US.Cl 318/685, 318/653, 318/659 Int. Cl. G05b 19/40 Field of Search318/685, 647, 653,

References Cited UNITED STATES PATENTS 3,012,177 Mortimer 318/653 X June26, 1973 2,855,551 10/1958 McCarty 318/653 X 2,957,115 10/1960 Clark eta1... 318/653 X 3,418,547 12/1968 Dudler 318/685 X 3,548,274 12/1970Mako 318/685 X 3,523,230 8/1970 York 318/685 X 3,448,362 6/1969 Dorf eta1. 318/685 3,486,091 12/1969 Siess 318/685 X Primary Examiner-T. E.Lynch AttorneyChittick, Pfund, Birch, Samuels & Gauthier [5 7] ABSTRACTA servo mechanism utilizing a pulse motor comprises a comparatoramplifier for producing an output corresponding to the differencebetween an input signal voltage and a feedback voltage, a signalconversion circuit for converting the output from the comparatoramplifier into two bit level signals, and a pulse motor driving circuitfor controlling the direction of the pulse motor in accordance with oneof the two bit level signals and for controlling the start and stop ofthe pulse motor in accordance with the other of the two bit levelsignals.

3 Claims, 8 Drawing Figures 4, COMPARATOR AMP.

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MEI 5 Bf 6 RIIFTQLFLITFL J E i /E F r INVENTOR ATTORNEY S PATENTEDJUH 26ms 3. 742.328 sum 8 or 6 F/GcS N INVERTER EXCLUSIVE GATES OR CIRCUIT n,n2 m f 9 EUR:

Q55 CLOCK PULSE GEN 65: I5: be I K051 I g C 52 I52 CP FF d n 54 I D Q54I FLIP-FLOP EORZ 0!,

l N VENTOR SUSUMU OHTA ATTORNEY 5 CLOSED LOOP STEPPING MOTORSERVO-MECHANISM BACKGROUND OF THE INVENTION This invention relates to aservo-mechanism suitable for use in an automatic balancing typerecording meter and the like, and particularly to a servo-mechanismcomprising a comparator amplifier productive of an output correspondingto the difference between an input signal voltage and a feedbackvoltage, a circuit for driving a pulse motor in accordance with theoutput of the said comparator amplifier, and a circuit to control thesaid feedback voltage by the rotation of the said pulse motor, in orderto attain a rotation angle of the said pulse motor corresponding to theinput signal voltage, balancing the said feedback voltage and the saidinput signal voltage.

Of late, a linear [C of a differential input, high both in quality anddependability, is easily available. Thus, if such a linear IC can beused as a comparator amplifier of a servo-mechanism, a small sizedservomechanism of high quality and dependability, utilizing thecharacteristics of an [C can be expected. But as well known, with alinear IC of a differential input, both positive and negative electricsources such as rHZV and -l2V with a base level for calculation as OVhave to be provided, which result is disadvantageous by complicating theelectric source circuit. The disadvantage becomes a problem particularlywhen the servomechanism is to be driven by a single, direct electriccurrent source.

Also, when a standard permanent magnet is used as the movable part of acircuit as a feedback voltage producing circuit, no-contact and nomanual operation can be realized for stabilization in contrast with anoperation utilizing a slide resistance, but it will require a separate,alternate electric current source for the magnet or an oscillator toresult in enlarging and complicating the device.

SUMMARY OF THE INVENTION The main purpose of the present invention is inachieving a servo-mechanism of simple construction with high quality anddependability by utilizing for a comparator amplifier a linear [C of adifferential input and utilizing a feedback voltage producing circuitwith a standard permanent magnet as the movable part.

Another purpose of the present invention is in attaining aservo-mechanism which can be driven by a single, direct electric currentsource.

Still another purpose of the present invention is in providing aservo-mechanism which is not affected by the common mode noise addedbetween the base side of the input signal voltage and the earth.

According to this invention, there is provided a servo-mechanismcomprising a comparator amplifier for producing an output correspondingto the difference between an input signal voltage and a feedbackvoltage, a signal conversion circuit for converting the output of thecomparator amplifier into two bit level signals, and a pulse motordriving circuit for controlling the direction of rotation of a pulsemotor in accordance with one of the two bit level signals and forcontrolling the start and stop of the pulse motor in accordance with theother of the two bit level signals.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block connectiondiagram of one embodiment of the novel servo-mechanism;

FIGS. 2 and 3 show graphs to explain the operation of the embodimentshown in FIG. 1;

FIG. 4 shows a block connection diagram of a modified embodiment of thisinvention;

FIGS. 5 and 6 show graphs to explain the operation of the embodimentshown in FIG. 4;

FIG. 7 shows one example of the magnetic converter utilized in theservo-mechanism of this invention; and

FIG. 8 shows a block connection diagram of a modified servo-motordriving circuit utilized in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of theaccompanying drawing, the servo-mechanism shown therein comprises aninput terminal 1 connected to receive an input signal voltage Ei, acircuit 2 for generating a feedback voltage Ef shown as comprising apotentiometer resistor R and a comparator amplifier 3 for providing anoutput E in accordance with the difference between input signal voltageEi and feedback voltage Ef. A linear integrated circuit with adifferential input is suitable for the comparator amplifier 3. Further,there is provided a signal converter 4 for converting the output E ofamplifier into a two bit level signal. The signal converter 4 comprisesan inverter I protective resistor R (because the output E of amplifier 3goes to the negative polarity), a NAND gate circuit G and a Zener diodeD for shifting the level. Denoting the threshold voltage of the inverterI by V due to the voltage drop V across protective resistor R caused bythe gate current, the apparent threshold voltage V will be expressed byFurther, by denoting the Zener voltage of Zener diode Dz. for levelshifting by Vz the apparent threshold voltage V of the NAND gate circuitG will be given y Accordingly, the relationship among the output a ofinverter 1 the output b of NAND gate G and the output E of comparatoramplifier 3, 6v the differential input e= (Ei Ef) can be shown by agraph shown in FIG. 2.

Assuming now about 8 volts for the threshold voltages of inverter I andfor the NAND gate G and about 12 volts for the Zener voltage V of Zenerdiode Dz then the apparent threshold voltage V will be about 5 voltswhereas V will be about 4 volts and the insensitive band of thecomparator amplifier 3 will be 9m V in terms of the input, provided thatthe gain of the comparator amplier 3 is assumed to be equal to 1,000.The inverter output a is used to control the direction of rotation of apulse motor to be described later whereas the output b from the NANDgate circuit is used to control the rotation and stopping of the pulsemotor.

The servo-mechanism further includes a circuit 5 for driving a pulsemotor 6, comprising a clock pulse generator CP for generating a clockpulse 0, a flip-flop circuit FF which generates a rectangular waveoutput (1 which reverses its polarity each time the Flip-Flop circuitreceives a clock pulse 0, and exclusive OR circuits EOR and EORResponsive, to the inverter output a of the signal conversion circuit 4applied to one input, the exclusive OR circuit EOR generates an output eof the rectangular waveform which is in phase or out-ofphase with theclock pulse impressed upon the other input, and responsive to the outpute from the exclusive OR circuit EOR applied to one input, the otherexclusive OR circuit EOR controls the phase of the output d from theflip-flop circuit FF to produce a rectangular waveform output f at itsoutput which is 90 advanced over the output d where output e and clockpulse c are in phase, whereas 90 delayed from the output d where outpute and clock pulse 0 are out-of-phase, Accordingly, rectangular outputs dand f from flip-flop circuit FF and exclusive OR circuit EOR form twophase rectangular waveforms which are synchronized with the clock pulsec and whose phase relationship is controlled by the inverter output a,as shown in FIG. 3. The driving circuit further includes NAND gatecircuits G through G with one of their inputs commonly supplied with theoutput b from the NAND gate circuit G of the signal conversion circuit4. The other input of NAND gate circuit G is coupled with the output dof flip-flop circuit FF, the input of NAND gate circuit G with theoutput f of exclusive OR gate circuit EOR whereas'the other inputs ofNAND gate circuits G and G are coupled respectively with the output g ofNAND gate circuit G and the output h of NAND gate circuit G The outputsg to j of these NAND gate cir cuits G through G provide rectangular waveoutputs whose direction of phase rotation is positive or negativedependent upon the level of inverter output a of the signal conversioncircuit 4 under control of the phase relationship between the two phaserectangular wave outputs d and f where the output b from NAND gatecircuit of the signal conversion circuit 4 has a unity level, as shownin FIG. 3. More particularly, when the level of the inverter outputdecreases to zero the rectangular outputs g through j establish an orderof phase rotation g h i j whereas when the level of the inverter outputa reaches unity the order of phase rotation will become j ih g. When thelevel of the NAND gate output B of the signal conversion circuit 4decreases to zero the outputs g through j of all NAND gate circuitsbecome unity.

One end of each of the exciting coils n through n, of a pulse motor 6 iscommonly connected to a plus source terminal +Es whereas the other endsare connected to the outputs of respective NAND gate circuits G throughG As shown by dotted lines, the shaft of pulse motor 6 is connected tothe sliding arm or brush of potentiometer resistor R For the purpose ofabsorbing the reverse electromotive forces diodes D through D areconnected in parallel with exciting coils n, to m, respectively.

The servo-mechanism of this invention operates as follows. Assume nowthat input signal voltage Ei is larger than feedback voltage Ef so thatthe difference 6 is positive and the output E of the comparatoramplifier 3 exceeds a reference value V Then-the inverter output a ofsignal conversion circuit 4 becomes zero whereas output b of the NANDgate circuit G becomes unity. Accordingly, the order of phase rotationof rectangular outputs g toj from pulse motor driving circuit 5 becomesg h i j whereby the exciting coils of the pulse motor is energized inthe order of n n n;, n thus driving the pulse motor 6 in the clockwisedirection. This rotation drives the brush of potentiometer R in adirection to increase the feedback voltage Ef until input signal voltageEi and feedback voltage Ef balance each other to reduce the differencevoltage e to zero. At this time, the output E from the comparatoramplifier 3 satisfies a relation VT 2 E0 5 VTW' thus decreasing thelevel of the NAND gate output b of the signal conversion circuit 4 tozero. Consequently, one input to all NAN D gate circuits G through G ofthe pulse motor driving circuit 5 becomes zero thus stopping pulse motor10. At this time, since no current flows through exciting coils n to n,of the pulse motor 6 it does not consume any power under the balancedcondition. When the input signal voltage Ei becomes smaller than thefeedback voltage Ef so that the difference voltage becomes negative andthe output E from the comparator amplifier 3 becomes smaller than thereference voltage V both of the inverter output a and the level of theNAND gate output b become unity. As a result, the order of phaserotation of the rectangular waveform outputs 3 through j of pulse motordrive circuit 5 will becomej ih g and the exciting coils of pulse motor6 energized in the order of n, n n n thus driving the pulse motor in thecounterclockwise direction. Again the motor drives the brush of thepotentiometer resistor R until feedback voltage Ef and input signalvoltage Ei balance each other. Upon reaching the balanced condition, theoutput E from comparator amplifier 3 becomes to a value satisfying arelation V 2 E 2 V and the level of the NAND gate output becomes zerothus stopping the pulse motor 6. In this manner, the position at whichpulse motor 6 comes to stop always corresponds correctly to the inputsignal voltage.

In this manner, the start and stop of the pulse motor is controlled byone bit level signal of two bit level signals from the signal conversioncircuit 4 while the direction of rotation of the pulse motor iscontrolled by the other one bit level signal so that the starting andstopping operations of the pulse motor are greatly stabilized.

A modified servo-mechanism shown in FIG. 4 also comprises an inputterminal l for receiving an input signal voltage Ei, a circuit 2 forgenerating a feedback voltage Ef, a comparator amplifier 3 for comparinginput signal voltage Ei and feedback voltage Ef and amplifying thedifference between them, a signal conversion circuit 4 for convertingthe output from the ,comparator amplifier into a two bit output levelsignal, a circuit 5 for driving a pulse motor in response to the two bitlevel signal from the signal conversion circuit, a pulse motor 6 and asource circuit 7.

Source circuit 7 comprises a DC source Es of 24 volts for example, whichis the sole source of the servomechanism, and a transistor Q10 whichfunctions as a voltage regulator. The collector electrode of transistorQ is connected to the positive pole of the source Es, the emitterelectrode is connected to the grounded negative pole of the source via acapacitor C and the base electrode is connected to the juncture betweena resistor R and a Zener diode D which are connected in series acrossthe source Es to supply a stable constant bias voltage 1-3,, of 12 voltsfor example. Conductors 1, and 11 are connected to the negative andpositive poles,

respectively, of the source and a common conductor 1 is supplied withthe bias voltage E The circuit 2 for generating feedback voltage Efcomprises a magnetically balanced type displacementelectric quantityconverter. More particularly, it comprises a magnetic converterincluding a saturable core T of Permaloy, for example, a movablepermanent magnet M, an exciting coil Wb, a detecting coil Wd and afeedback coil Wf. These coils are wound on saturable core T and movablepermanent magnet M is connected to the shaft of a pulse motor 6 is shownby dotted lines.

One example of the construction of the magnetic converter 21 isillustrated in FIG. 7. As shown, core T takes a form of an annular ringand a pair of diametrically opposing pole pieces with their inner endssurrounding the movable permanent magnet M. The feedback coil Wfanddetecting coil Wd each comprises two sectrons connected in seriesopposition whereas the exciting coil Wb comprises two sections connectedin series cummulatively. The output from the detecting coil Wd isamplified by a transistor Q21. The base electrode of this transistor Qis connected to a resonance circuit comprised by detecting coil Wd and acapacitor C the collector electrode is connected to a resistor R and theemitter electrode to a resistor R through parallel connected resistor Rand capacitor C Resistor R and diodes D and D provide a bias potentialfor transistor Q21- Thc driving voltage for this amplifier is suppliedfrom a Zener diode Dz connected across conductors 1 and 1 via a resistorR A capacitor C is connected across Zener diode Dz, for by-pasing ACcomponents. There is provided a rectifying and smoothing circuit 23comprising a rectifier including diodes D and D and a resistor R whichare connected in series, and a capacitor for connecting the juncturebetween diodes D and D to the colector electrode of transistor Q and asmoothing circuit including a resistor R, and capacitors C and Cconnected to the opposite terminals of resistor R Circuit 2 furtherincludes .a DC amplifier 24 comprising transistors Q and Q connected inthe form of a Darlington connection. The base electrode of transistor Qis connected to the smoothing circuit and the emitter electrode oftransistor Q is connected to common line 1;, through the feedback coilWf and a load resistor R,,. The collector electrode of transistor O isconnected to conductor 1 through resistor R If there is a differ enceAd) between the flux M produced by movable permanent magnet M and theflux f produced by the current flowing through the feedback coil Wf, anAC voltage will be induced in detecting coil Wd, which is amplified bytransistor Q and the half wave of the output current, that is theemitter current of transistor 0,, is positively fed back to excitingcoil Wb. Consequently, a loop comprising magnetic converter 21, theresonance circuit, amplifier 22 constituted by transistor 0,, and thepositive feedback circuit oscillates under self excitation with afrequency determined by the constant of resonance circuit and anamplitude propotional to the difference in the flux A. When the polarityof difference flux Ad; reverses, the oscillation amplifier circuit stopsoscillation. The output of the oscillation amplifier circuit isrectified by the rectifying and smoothing circuit 23 and is thenamplified by DC amplifier 24 to provide an output DC I The outputcurrent I flows through feedback coil Wf to decrease the difference fluxAdv. Since the gain of the oscillation amplifier circuit is sufficientlylarge, the difference in flux Ad) is reduced to substantially zero thusbalancing fluxes M and f. Thus, the output current I of the DC amplifiercircuit 24 accurately corresponds to the displacement of the movablepermanent magnet M. Output current I flows through load resistor R toproduce a feedback voltage Ef across the load resistor. In this manner,when the feedback voltage generating circuit 2 is comprised by amagnetically balanced type displacement-electric quantity converter itis possible to use a permanent magnet as the movable element. Thus, theconverter can be constructed as a contactless type operating stably andreliably. Further, when the dis placement-electric quantity converter iscomprised by a self excitation oscillation amplifier circuit as abovedescribed it is not necessary to use any additional AC source oroscillator thus greatly simplifying the construction. Thus, theservo-mechanism can be operated solely by a DC source. Instead ofenergizing the feedback voltage generating circuit with the voltagebetween lines 1 and 1,, the voltage between lines 1 and 1 can also beused. In the latter case, it is not only possible to decrease thecurrent taken from source Es by an amount equal to the current flowingthrough the feedback voltage generating circuit but also toproportionally decrease the heating of transistor Q comprising theregulator circuit.

For the comparator circuit 3 shown in FIG. 4, is used an operationalamplifier having a differential input and constructed as a linearintergrated circuit. The positive and negative input terminals ofoperational amplifier 3 are connected to input terminals 1 throughresistors R and R to receive input signal voltage Ei. The positive inputterminal is also connected to a load resistor R in the feedback voltagegenerating circuit 2 through resistor R thus appling the feedbackvoltage Ef to the positive input terminal. On the other hand, thenegative input terminal of amplifier 3 is connected to a midpoint ofpotentiometer resistors R and R via a resistor R so as to negativelyfeedback the output of amplifier 3 to its negative input terminal. Thesource terminals of the opterional amplifier 3 are connected acrosslines 1 and I, to directly receive a voltage of 24 volts from source Es.By the connection described above, the bias voltage E, is applied to thepositive input terminal of amplifier 3 to bring the potential of theinput terminal to the reference level so that lines 1, and 1 assumepotentials of +24V and 0V respectively with respect to the referencelevel E This arrangement enables one to drive the operational amplifier3 with the single DC source Es which otherwise requires two sources'ofpositive and negative. Consequently, an output voltage E expressed bythe following equation appears on the output terminal of the operationalamplifier where Ex represents the potential difference between thenegative side of the input terminals receiving the input signal voltageEi and the 0V conductor 1,. Assuming that 31 32 33 34 R, and 35 as) ss Kthen the output voltage E can be rewritten as E =K(EiEf)E This relationis plotted in FIG. A. In this manner, when the input signal voltage Eiis applied to the differential operational amplifier, it is possible toeliminate the term Ex as shown by equation 3, so as to eliminate theeffect of the voltage drop in the common line caused by the currentdrawn from the source. Even when the input signal voltage Ei deviatesfrom 0V, such deviation does not affect the output thus enabling one toderive out the input signal voltage Ei from any desired level.

The base electrode of transistor Q, of the signal conversion circuit 4is connected to the juncture between potentiometer resistors R and Rwhich are connected in series across the output terminal of opera tionalamplifier 3 and 0V conductor 1, and the collector electrode is connectedto conductor 1;, through a resistor R The emitter electrode is connectedto the OV conductor 1,.

Accordingly, transistor Q41 becomes conductive when the output E, fromthe operational amplifier exceeds a reference voltage m V that isdetermined by the ratio l/m of potentiometer resistors R and R and thebase-emitter voltage V The base electrode of another transistor Q isconnected to the juncture between potentiometer resistors R. and R whichare connected in series across the output terminal of the operationalamplifier 3 and 0V conductor 1,. The collector electrode of transistor Qis connected to common conductor 1 through a resistor R while theemitter electrode is connected to the OV conductor 1 Similar totransistor Q transistor Q becomes conductive when the output E of theoperational amplifier exceeds a reference voltage nV which is determinedby the ratio l/n of potentiometer resistors R and R and the base-emittervoltage V When transistors Q, and Q42 are conductive, their collectorpotentials become zero whereas when they are nonconductive, theircollector potentials become E Thus, assuming that zero volt denotes thelevel of zero and that E denotes the level of one, the collectorelectrodes of transistors Q and Q42 will produce signals of the level 0and 1, respectively, as shown in FIG. 5 in accordance with the result ofcomprarison of the output E from the operational amplifier and thereference voltages. The level signal appearing at the collectorelectrode of transistor 0 is applied to an inverter I whereas the levelsignal appearing at the collector electrode of transistor 0 is appliedto one input of a NAND gate circuit G The output from inverter I isapplied to the other input of NAND gate circuit G As a result, theoutput a of the inverter and the output b of the NAND gate circuitdepend upon the magnitude E of the operational amplifier 3, as shown inFIG. 5D and FIG. 5E, respectively. The inverter output a is used tocontrol the direction of rotation of pulse motor 6 whereas the output bof the NA ND gate circuit is used to control the start and stop of thepulse motor 6.

In this manner, provision of transistors Q and Q before inverter I andNAND gate circuit 0, of the signal conversion circuit assures morepositive operation. The output of either transistor Q of Q may besubstituted for the output of inverter I which acts as the level signalfor controlling the direction of rotation of the pulse motor. Further,instead of utilizing the voltage of the 0V conductor 1 1 as thereference for the signal conversion circuit 4, the voltage of the commonconductor 1 can also be used. In the latter case, however, it isnecessary to provide a suitable protective circuit in order to protectthe base-emitter junctions of transistors Q41 and Q42 against a largenegative value of the output E of the operational amplifier 3.

With reference now to the pulse motor driving circuit 5, it comprises aclock pulse generator CP for generating a clock pulse 0, a flip-flopcircuit FF for producing a rectangular wave output d which reverses itspolarity at each clock pulse c and exclusive OR gate circuits EOR, andEOR Exclusive OR gate circuit EOR, functions to produce a rectangularwave output e which is in phase or out-of-phase with the flip-flopoutput d impressed upon one input terminal in accordance with theinverter output a of the signal conversion circuit 4 which is impressedupon the other input terminal of the exclusive OR gate circuit EOR,. Onthe other hand, the other exclusive OR gate circuit EOR produces arectangular wave output f phase advanced than the flipflop output dimpressed upon its one input terminal. Consequently, as shown in FIG. 6,the rectangular wave outputs e and f of the exclusive OR gate circuitsEOR and EOR are two phase rectangular waves which are synchronized withthe clock pulse 0 and controlled their phase relationship by theinverter output a.

The circuit 5 further includes NAND gate circuits G through G with theirone input terminals commonly connected to receive the output b from theNAND gate circuit G of the signal conversion circuit 4. The other inputof NAND gate circuit G is supplied with the output e of the exclusive ORgate circuit EOR and the other input of NAND gate circuit G is suppliedwith the output f of the exclusive OR circuit EOR The other inputs ofNAND gate circuits G and G are supplied with outputs g and h of NANDgate circuits G and G respectively. Outputs g throughj of these NANDgate circuits form rectangular wave outputs having a forward or reversephase rotation as shown in FIG. 6 dependent upon the phase relationshipbetween the outputs e and f of the exclusive OR gate circuits or thelevel of the inverter output a of the signal conversion circuit wherethe level of the output I of the NAND gate circuit in the signalconversion circuit 4 equals 1. In other words, when the level of theinverter output a equals 0, the order of the phase rotation of therectangular wave outputs g through j is g h i j, whereas where the levelof the inverter output a equals 1 the order of the phase rotationbecomes j i h.

g. When the level of the NAND gate output b of the signal conversioncircuit 4 becomes 0 all outputs g through j of NAND gate circuits Gthrouth G become I.

Further, there are provided transistors Q51 through Q with their baseelectrodes connected to the outputs of NAND gate circuits G to Grespectively, through inverters 1 through I The emitter electrodes ofthese transistors are connected to OV conductor 1, whereas collectorelectrodes are connected to 24 V conductor 1 through exciting coils n ton,, respectively, of the pulse motor 6. With this connection, when thelevel of the NAND gate output B of the signal conversion circuit 4becomes 1, the triggering point of transistors Q to Q are sequentiallyshifted in accordance with the rectangular wave outputs g through jwhose order of phase rotation is controlled by the inverter output a andwhen the level of the NAND gate output b of the signal conversioncircuit 4 becomes 0, all of these transistors become OFF.

Although the driving source for these logic circuits is not shown in thedrawing, it is to be understood that such source is connected acrossconductors 1 and 1 Since the outputs of NAND gate circuits G to G areapplied to pulse motor 6 through transistors O to Q it is possible toincrease the load of the pulse motor motor than in the case withoutthese transistors. In the two phase rectangular wave generating circuitof the pulse motor driving circuit 5, the connection of the output d ofthe flip-flop circuit FF and the output f of the exclusive OR gatecircuit EOR may be interchanged. In other words, the output f from theexclusive OR gate circuit EOR may be applied to the exclusive OR gatecircuit EOR so as to use the output e from the exclusive OR gate circuitEOR, and the output d from the flip-flop circuit FF as the two phaserectangular wave signals.

FIG. 8 shows a modified embodiment of the pulse motor driving circuit 5in which the clock pulse generator CP and flip-flop circuit FF are resetwhen the level of the output b from the NAND gate circuit in the signalconversion circuit 4 becomes 0. In this embodiment, only two NAND gatecircuits G and G suffice.

The servo-mechanism shown in FIG. 4 operates in the same manner as thefirst embodiment shown in FIG. 1. More particularly, when the inputsignal voltage Ei is smaller than the feedback voltage Ef, so thedifference e is negative and when the output E of the operationalamplifier 3 is smaller than the reference m V 'the level of the inverteroutput a of the signal conversion circuit 4 will become 0 and that ofthe NAND gate output will become 1. Accordingly, the order of phaserotation of the rectangular wave outputs g through j of the pulse motordriving circuit will be g h i j thus successively rendering ONtransistors Q through Q according to the order of Q Q 05;, QAccordingly, the exciting coils of the pulse motor 6 are energized inthe order of '1 n n n, thus driving the motor in the clockwisedirection. As a result,-the permanent magnet M is rotated in a directionto decrease feedback voltage Ef so as to balance the input signalvoltage Ei to reduce the difference voltage 5 to substantially zero. Atthis time, the output E of the operational amplier satisfies a conditionn V 2 E m V so that the level of the NAND gate output b of the signalconversion circuit 4 becomes 0. Thus, all transistors Q through 0 in thepulse motor driving circuit 5 are rendered OFF to stop the rotation ofthe pulse motor. In this manner, since no current flows through theexciting coils n, to n, of the motor, the motor consumes no power underthe balanced condition. When the input signal voltage Ei exceeds thefeedback voltage Ef so that the difference voltage e becomes positiveand the output E, from operational amplifier 3 exceeds the referencevalue n V then the levels of both inverter output a in the signalconversion circuit 4 and the NAND gate output b become 1. Then,

the order of phase rotation of the rectangular wave outputs g toj of thepulse motor driving circuit 4 becomes j i -*h g so that the transistorsQ to 0 are sequentially turned on in the order of Q Q Q Q with theresult that the exciting coils of the pulse motor 6 are excited in theorder of n, n n m, thus rotating the pulse motor in the counterclockwisedirection. Similar to the rotation in the clockwise direction, thiscounterclockwise rotation of the permanent magnet M varies the feedbackvoltage to balance with the input signal voltage Ei. Under the balancedcondition, the output E, from the operational amplifier satisfies arelation n V 3 E E m V whereby the level of the NAND gate output bbecomes 0 to stop the rotation of the pulse motor 6. Thus, the motor isstopped at a position precisely corresponding to the value of the inputsignal voltage Ei.

While in the foregoing embodiment, the signal conversion circuit 4 wasshown to comprise potentiometer resistors, transistors, an inverter anda NAND gate circuit, it is to be understood that the invention is by nomeans limited to this particular construction, and that any circuit thatcompares the output from the opera tional amplifier with a referencevalue to generate two bit level signals can also be used as the signalconversion circuit. Likewise, any circuit that can control the directionof rotation of the pulse motor by one of two bit level signals generatedby the signal conversion circuit and can control the start and stop ofthe pulse motor by the other of the two bit level signals can also beused as the pulse motor driving circuit 5.

While the invention has been shown and described in terms of somepreferred embodiment thereof, it should be understood that many changesand modifications may be made without departing from the scope of theinvention as defined in the appended claims.

What is claimed is:

l. A servo-mechanism for driving a pulse motor including a comparatoramplifier for producing an output corresponding to the differencebetween an input sig nal voltage and a feedback voltage, a circuit fordriving said pulse motor in accordance with the output of the saidcomparator amplifier, and circuit means for producing said feedbackvoltage by the rotation of the said pulse motor in order to attain arotation angle of the said pulse motor corresponding to the input signalvoltage, thereby balancing said feedback voltage and said input signalvoltage, in which:

said comparator amplifier comprises a linear integrated circuitamplifier with differential input, a single direct electric currentsource connected to supply the source terminal of said integratedcircuit amplifier, and

a bias voltage attained from said single direct electric current sourceapplied to be the base electric potential level for operation of saidintegrated circuit amplifier; and

said circuit means for producing said feedback voltage comprises amagnetic convertor having a magnetic core wound with an exciting coil, adetection coil and a feedback coil, and a movable permanent magnet whichis displaced by said pulse motor,

means including a tuned amplifier for amplifying the output signal atsaid detection coil, for applying the half wave alternate output of thesaid tuned amplifier as positive feedback to said feedback coil to forma self-oscillating tuned amplifier circuit in order to attain an outputvoltage corresponding to the degree of displacement of the said movablepermanent magnet,

means responsive to said output voltage and operative to apply anegative feedback current to said feedback coil in accordance with therectified output voltage of said self-oscillating tuned amplifier forbalancing the magnetic flux from said movable permanent magnet, and

means for developing said feedback voltage from said feedback currentand applying said feedback voltage in opposition to said input signalvoltage at said differential input.

2. The servo-mechanism according to claim 1, arranged for common modesuppression wherein said comparator amplifier has said input signalvoltage applied between its differential inputs, said feedback voltageis applied to only one of said differential inputs, and said biasvoltage is applied to said one differential input, and means forapplying the output of said comparator amplifier as negative feedback tothe other of its differential inputs.

3. The servo-mechanism, according to claim 1, and further including asignal conversion circuit for converting the output of said comparatoramplifier into two bit level signals, a circuit for generating a twophase rectangular wave signal whose relative phase is controlled inaccordance with one of said two bit level signals, a gate circuitcontrolled in accordance with the other one of said two bit levelsignals, and wherein said circuit for driving said pulse motor isresponsive to said relative phase of said two phase rectangular wavesignal for controlling the direction of rotation of said pulse motor andresponsive to said gate circuit for controlling the start and stop ofsaid pulse motor.

P040 UNITED STATES PATENT omen CER I ll [CA1 L 01* CORRLC 1 MN PatentNo. 3 r 742 r Dated June 26 I 1973 Inventor) Susumu Ohta L It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

F- Column 5, line 32, "by-pasing" should be by-passing I Column 5, line37, "colector" should be collector Column 6, line 45, "opterional"should be operational Column7, line 7,"E K (Ei Ef) E should be E0 K (EiEf) EB Column 7, line 53, "comprarison" should be comparison Column 8,line 4, "of" should be or Signed and sealed this 3rd day of September1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents- UNITED STATES PATENT OFFICE CER'IHILAHJ O1 LOlUULCllU'N PatentNo. r 4 ,328 Dated June 3 Inventor) Sus umu Ohta It is certified thaterror appears in the above'identificd patent and that said LettersPatent are hereby corrected as shown below:

r Column 5, line 32, "by-pasing" should be by-passing *1 Column 5, line37, "colector" should be collector Column 6, line 45, "opterional"should be operational fColumn 7, line '7, "JE K (Ei Ef) E should be s6 K(Ei Ef) E Column 7, line 53, "comprarison" should be comparison Column8, line 4, "of" should be or Signed and'sealed this 3rd day of September1974.

Attest:

MCCOY MQ GIBSON, JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents-

1. A servo-mechanism for driving a pulse motor including a comparatoramplifier for producing an output corresponding to the differencebetween an input signal voltage and a feedback voltage, a circuit fordriving said pulse motor in accordance with the output of the saidcomparator amplifier, and circuit means for producing said feedbackvoltage by the rotation of the said pulse motor in order to attain arotation angle of the said pulse motor corresponding to the input signalvoltage, thereby balancing said feedback voltage and said input signalvoltage, in which: said comparator amplifier comprises a linearintegrated circuit amplifier with differential input, a single directelectric current source connected to supply the source terminal of saidintegrated circuit amplifier, and a bias voltage attained from saidsingle direct electric current source applied to be the base electricpotential level for operation of said integrated circuit amplifier; andsaid circuit means for producing said feedback voltage comprises amagnetic convertor having a magnetic core wound with an exciting coil, adetection coil and a feedback coil, and a movable permanent magnet whichis displaced by said pulse motor, means including a tuned amplifier foramplifying the output signal at said detection coil, for applying thehalf wave alternate output of the said tuned amplifier as positivefeedback to said feedback coil to form a self-oscillating tunedamplifier circuit in order to attain an output voltage corresponding tothe degree of displacement of the said movable permanent magnet, Meansresponsive to said output voltage and operative to apply a negativefeedback current to said feedback coil in accordance with the rectifiedoutput voltage of said selfoscillating tuned amplifier for balancing themagnetic flux from said movable permanent magnet, and means fordeveloping said feedback voltage from said feedback current and applyingsaid feedback voltage in opposition to said input signal voltage at saiddifferential input.
 2. The servo-mechanism according to claim 1,arranged for common mode suppression wherein said comparator amplifierhas said input signal voltage applied between its differential inputs,said feedback voltage is applied to only one of said differentialinputs, and said bias voltage is applied to said one differential input,and means for applying the output of said comparator amplifier asnegative feedback to the other of its differential inputs.
 3. Theservo-mechanism, according to claim 1, and further including a signalconversion circuit for converting the output of said comparatoramplifier into two bit level signals, a circuit for generating a twophase rectangular wave signal whose relative phase is controlled inaccordance with one of said two bit level signals, a gate circuitcontrolled in accordance with the other one of said two bit levelsignals, and wherein said circuit for driving said pulse motor isresponsive to said relative phase of said two phase rectangular wavesignal for controlling the direction of rotation of said pulse motor andresponsive to said gate circuit for controlling the start and stop ofsaid pulse motor.